1 files changed, 131 insertions, 0 deletions
diff --git a/src/StardewModdingAPI/Utilities/SDate.cs b/src/StardewModdingAPI/Utilities/SDate.cs
new file mode 100644
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+++ b/src/StardewModdingAPI/Utilities/SDate.cs
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+using System;
+using System.Linq;
+using StardewValley;
+
+namespace StardewModdingAPI.Utilities
+{
+    /// <summary>Represents a Stardew Valley date.</summary>
+    public class SDate
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The internal season names in order.</summary>
+        private readonly string[] Seasons = { "spring", "summer", "fall", "winter" };
+
+        /// <summary>The number of days in a season.</summary>
+        private readonly int DaysInSeason = 28;
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The day of month.</summary>
+        public int Day { get; }
+
+        /// <summary>The season name.</summary>
+        public string Season { get; }
+
+        /// <summary>The year.</summary>
+        public int Year { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="day">The day of month.</param>
+        /// <param name="season">The season name.</param>
+        /// <exception cref="ArgumentException">One of the arguments has an invalid value (like day 35).</exception>
+        public SDate(int day, string season)
+            : this(day, season, Game1.year) { }
+
+        /// <summary>Construct an instance.</summary>
+        /// <param name="day">The day of month.</param>
+        /// <param name="season">The season name.</param>
+        /// <param name="year">The year.</param>
+        /// <exception cref="ArgumentException">One of the arguments has an invalid value (like day 35).</exception>
+        public SDate(int day, string season, int year)
+        {
+            // validate
+            if (season == null)
+                throw new ArgumentNullException(nameof(season));
+            if (!this.Seasons.Contains(season))
+                throw new ArgumentException($"Unknown season '{season}', must be one of [{string.Join(", ", this.Seasons)}].");
+            if (day < 1 || day > this.DaysInSeason)
+                throw new ArgumentException($"Invalid day '{day}', must be a value from 1 to {this.DaysInSeason}.");
+            if (year < 1)
+                throw new ArgumentException($"Invalid year '{year}', must be at least 1.");
+
+            // initialise
+            this.Day = day;
+            this.Season = season;
+            this.Year = year;
+        }
+
+        /// <summary>Get a new date with the given number of days added.</summary>
+        /// <param name="offset">The number of days to add.</param>
+        /// <returns>Returns the resulting date.</returns>
+        /// <exception cref="ArithmeticException">The offset would result in an invalid date (like year 0).</exception>
+        public SDate AddDays(int offset)
+        {
+            // simple case
+            int day = this.Day + offset;
+            string season = this.Season;
+            int year = this.Year;
+
+            // handle season transition
+            if (day > this.DaysInSeason || day < 1)
+            {
+                // get current season index
+                int curSeasonIndex = Array.IndexOf(this.Seasons, this.Season);
+                if (curSeasonIndex == -1)
+                    throw new InvalidOperationException($"The current season '{this.Season}' wasn't recognised.");
+
+                // get season offset
+                int seasonOffset = day / this.DaysInSeason;
+                if (day < 1)
+                    seasonOffset -= 1;
+
+                // get new date
+                day = this.GetWrappedIndex(day, this.DaysInSeason);
+                season = this.Seasons[this.GetWrappedIndex(curSeasonIndex + seasonOffset, this.Seasons.Length)];
+                year += seasonOffset / this.Seasons.Length;
+            }
+
+            // validate
+            if(year < 1)
+                throw new ArithmeticException($"Adding {offset} days to {this} would result in invalid date {day:00} {season} {year}.");
+
+            // return new date
+            return new SDate(day, season, year);
+        }
+
+        /// <summary>Get a string representation of the date. This is mainly intended for debugging or console messages.</summary>
+        public override string ToString()
+        {
+            return $"{this.Day:00} {this.Season} Y{this.Year}";
+        }
+
+        /// <summary>Get the current in-game date.</summary>
+        public static SDate Now()
+        {
+            return new SDate(Game1.dayOfMonth, Game1.currentSeason, Game1.year);
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Get the real index in an array which should be treated as a two-way loop.</summary>
+        /// <param name="index">The index in the looped array.</param>
+        /// <param name="length">The number of elements in the array.</param>
+        private int GetWrappedIndex(int index, int length)
+        {
+            int wrapped = index % length;
+            if (wrapped < 0)
+                wrapped += length;
+            return wrapped;
+        }
+    }
+}